1. Field of the Invention
The present invention relates to a Coriolis flow meter and method for determining flow characteristics, and more particularly, to a Coriolis flow meter and method for determining flow characteristics using two or more vibrational responses.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flow meters, typically operate by detecting motion of a vibrating conduit that contains a flowing material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flow meter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries and the like, in the system. Each conduit may be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations. Two such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to electronic instrumentation by cabling, such as two independent pairs of wires. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement.
Traditional Coriolis mass flow meters provide continuous measurement of the mass flow rate, density, and temperature of the flow medium flowing through the flow meter. However, a change in any of the flow characteristics of the flow medium can cause an increase or decrease in the mass loading on the flow meter, and hence will cause an error in the indicated density, among other things.
Designers of vibrating element transducers, such as Coriolis mass flow meters or densitometers, generally try to maximize the sensitivity of the mass, density, and temperature while minimizing the transducer sensitivity to the viscosity, VOS, shear rate, pressure, and Reynolds number. As a result, a typical prior art flow meter is capable of accurately measuring the mass, density, and temperature but is not capable of accurately measuring additional flow characteristics such as one or more of the viscosity, VOS, shear rate, pressure, and Reynolds number. There is a need in flow meter applications to measure other flow characteristics in addition to mass, density, and temperature.